METHODS OF DEGRADING ORGANIC POLLUTANTS AND PREVENTING OR TREATING MICROBE USING Bi2S3-CdS PARTICLES

ABSTRACT

Methods of synthesizing Bi 2 S 3 —CdS particles in the form of spheres as well as properties of these Bi 2 S 3 —CdS particles are described. Methods of photocatalytic degradation of organic pollutants employing these Bi 2 S 3 —CdS particles and methods of preventing or reducing microbial growth on a surface by applying these Bi 2 S 3 —CdS particles in the form of a solution or an antimicrobial product onto the surface are also specified.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to Bi₂S₃—CdS particles in the form ofspheres, a method of preparing the Bi₂S₃—CdS particles, and methods ofemploying these Bi₂S₃—CdS particles for photocatalytically degradingorganic pollutants and for killing or inhibiting growth ofmicroorganisms.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Organic pollutants including dyes produced by the textile, printing, andpaper industries and during experimental uses may end up in wastewatersand pose a potential threat to the environment because of theircarcinogenic nature. For example, methyl orange, which is a frequentlyused azo dye, is considered mutagenic. Purification methods such aschemical precipitation and flocculation, and absorption have beendeveloped fir removing organic pollutants from wastewater.Photocatalytic degradation is a viable alternative for removing organicpollutants. Unlike physical processes such as adsorption, which simplyrelocate the organic pollutant from wastewater to the adsorbent andcause secondary contamination, photocatalytic degradation is a moreeffective strategy which can break down the organic pollutants on amolecular level and form carbon dioxide, water, and other less toxicmolecules. It is advantageous to develop nanomaterials exhibiting goodphotocatalytic degradation capabilities of organic pollutants.

The unique outer membrane of gram-negative bacteria protects them frommany antibiotics including penicillin, which leads to medical challengesin treating infections caused by these bacteria. For example, Klebsiellaorganisms, which are gram-negative bacteria often resistant to multipleantibiotics, have become important pathogens in nosocomial infections.Common conditions caused by Klebsiella bacteria include pneumonia,infections in the urinary tract, lower biliary tract, and surgical woundsites. Bacterial drug resistance may stem from the build-up ofantibiotics in the environment. Over usage and unnecessary prescriptionsof antibacterial drugs as well as capability of bacteria to adapt andevolve rapidly have contributed to the occurrence of antibioticresistance. Antibiotic-resistant pathogens have already caused millionsof illnesses and tens of thousands of deaths worldwide. Staphylococcusaureus (S. aureus) is one of the most common causes of bacteremia,infective endocarditis, bone and joint infections including infectionsfrom joint replacement surgeries, medical implant infections, variousskin and soft-tissue infections, animal infections, and food poisoning.In addition, the emergence of antibiotic-resistant strains of S. aureussuch as methicillin-resistant S. aureus (MRSA) is a worldwide problem inclinical medicine. Despite much research and development, no vaccine forS. aureus has been approved. It is beneficial to develop alternativenanomaterials possessing broad spectrum antimicrobial activities thatare effective on both gram-positive and gram-negative bacterial strains.

In view of the forgoing, one objective of the present disclosure is toprovide a method of photodegrading organic pollutants employingBi₂S₃—CdS particles. A second objective of the present disclosure is toprovide a method of preventing or reducing microbial growth on a surfaceby applying Bi₂S₃—CdS particles to the surface. A further objective ofthe present disclosure is to provide a method of preparing Bi₂S₃—CdSparticles.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a methodfor degrading an organic pollutant. The method involves (i) contactingBi₂S₃—CdS particles with an aqueous solution comprising the organicpollutant to form a mixture, and (ii) illuminating the mixture with alight at a wavelength in a range of 200-700 nm for 0.1-6 hours therebydegrading the organic pollutant, wherein the Bi₂S₃—CdS particlescomprise bismuth(III) sulfide and cadmium(II) sulfide, the Bi₂S₃—CdSparticles are in the form of spheres, and the organic pollutant ispresent in the aqueous solution at a concentration of 1-1,000 mg/Lrelative to a total volume of the aqueous solution.

In one embodiment, an atomic ratio of bismuth to cadmium in theBi₂S₃—CdS particles is in a range of 0.5:1 to 4:1, and an atomic ratioof sulfur to bismuth in the Bi₂S₃—CdS particles is in a range of 3:2 to8:1.

In one embodiment, the Bi₂S₃—CdS particles are in the form of sphereswith an average diameter of 0.3-5 μm.

In one embodiment, the Bi₂S₃—CdS particles have a BET surface area of5-25 m²/g, a pore size of 10-50 nm, and a pore volume of 0.02-0.2 cm³/g.

In one embodiment, an amount of the Bi₂S₃—CdS particles in the mixtureis in a range of 0.1-10 g/L relative to a total volume of the mixture.

In one embodiment, at least 30% of the organic pollutant is degradedwithin 2 hours of illuminating.

In one embodiment, the organic pollutant comprises methyl orange, methylgreen, or both.

According to a second aspect, the present disclosure relates to a methodfor preventing or reducing growth of a microorganism on a surface. Themethod involves applying Bi₂S₃—CdS particles onto the surface, whereinthe Bi₂S₃—CdS particles comprise bismuth(III) sulfide and cadmium(II)sulfide, the Bi₂S₃—CdS particles are in the form of spheres, and theBi₂S₃—CdS particles are in contact with the surface for 1-24 hours.

In one embodiment, an atomic ratio of bismuth to cadmium in theBi₂S₃—CdS particles is in a range of 0.5:1 to 4:1, and an atomic ratioof sulfur to bismuth in the Bi₂S₃—CdS particles is in a range of 3:2 to8:1.

In one embodiment, the Bi₂S₃—CdS particles have a BET surface area of5-25 m²/g, a pore size of 10-50 nm, and a pore volume of 0.02-0.2 cm³/g.

In one embodiment, the Bi₂S₃—CdS particles are applied onto the surfaceas a solution comprising a solvent and 1 μg/mL to 50 mg/mL of theBi₂S₃—CdS particles relative to a total volume of the solution.

In one embodiment, the solvent comprises dimethyl sulfoxide and water.

In one embodiment, the Bi₂S₃—CdS particles are applied onto the skin ofa subject as an antimicrobial cream comprising 0.01 wt %-50 wt % of theBi₂S₃—CdS particles relative to a total weight of the antimicrobialcream.

In one embodiment, the microorganism is at least one gram-negativebacterium selected from the group consisting of Acinetobacter baumannii,Enterobacter aerogenes, Escherchia coli, Klebsiella oxytoca andKlebsiella pneumoniae.

In one embodiment, the microorganism is at least one gram-positivebacterium selected from the group consisting of Staphylococcus aureus,Staphylococcus epidermis, and MRSA.

According to a third aspect, the present disclosure relates to Bi₂S₃—CdSparticles comprising bismuth(III) sulfide, and cadmium(II) sulfide,wherein the Bi₂S₃—CdS particles are in the form of spheres with anaverage diameter of 03-5 μm.

According to a fourth aspect, the present disclosure relates to a methodof preparing the Bi₂S₃—CdS particles of the third aspect. The methodinvolves (i) mixing a bismuth(III) salt, a cadmium(II) salt, and anoptionally substituted thiourea with a solvent in the presence ofpolyvinylpyrrolidone to form a reaction mixture, and (ii) heating thereaction mixture in an autoclave at a temperature of 100-300° C. for2-48 hours, thereby forming the Bi₂S₃—CdS particles.

In one embodiment, an atomic ratio of bismuth to cadmium in the reactionmixture is in a range of 0.5:1 to 4:1

In one embodiment, a molar ratio of the optionally substituted thioureato the bismuth(III) salt is in a range of 2:1 to 10:1.

In one embodiment, the optionally substituted thiourea is thiourea offormula SC(NH₂)₂.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is a scanning electron microscopy (SEM) image of Bi₂S₃—CdSnanospheres.

FIG. 1B is a high magnification SEM image of Bi₂S₃—CdS nanospheres.

FIG. 2 is an X-ray diffraction (XRD) pattern of Bi₂S₃—CdS nanospheres.

FIG. 3 is a UV-vis diffuse reflectance spectrum of Bi₂S₃—CdSnanospheres.

FIG. 4 shows changes in UV-vis absorption spectra demonstratingdegradation of methyl green in the presence of Bi₂S₃—CdS nanospheresunder different irradiation times.

FIG. 5 shows changes in UV-vis absorption spectra demonstratingdegradation of methyl orange in the presence of Bi₂S₃—CdS nanospheresunder different irradiation times.

FIG. 6 is a graph showing the photocatalytic activities of Bi₂S₃—CdSnanospheres degrading methyl green and methyl orange over a period of120 min.

FIG. 7 is a bar graph showing antibacterial activities represented byzone of inhibition of Bi₂S₃—CdS nanospheres at various concentrationsagainst gram-negative bacteria.

FIG. 8 is a bar graph showing antibacterial activities represented byzone of inhibition of Bi₂S₃—CdS nanospheres at various concentrationsagainst gram-positive bacteria.

FIG. 9 is a bar graph showing minimum bactericidal concentrations (MBCs)of Bi₂S₃—CdS nanospheres over gram-negative and gram-positive bacteriastrains.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in whichsome,but, not all embodiments of the disclosure are shown.

The present disclosure will be better understood with reference to thefollowing definitions.

As used herein, the words “a” and “an” and the like carry the meaning of“one or more.” Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

As used herein, the terms “compound” and “product” are usedinterchangeably, and are intended to refer to a chemical entity, whetherin the solid, liquid or gaseous phase, and whether in a crude mixture orpurified and isolated.

The present disclosure is intended to include all isotopes of atomsoccurring in the present compounds. Isotopes include those atoms havingthe same atomic number but different mass numbers. By way of generalexample, and without limitation, isotopes of hydrogen include deuteriumand tritium, isotopes of carbon include ¹³C and ¹⁴C, and isotopes ofsulfur include ³³S, ³⁴S, and ³⁶S. Isotopically labeled compounds of thedisclosure can generally be prepared by conventional techniques known tothose skilled in the art or by processes and methods analogous to thosedescribed herein, using an appropriate isotopically labeled reagent inplace of the non-labeled reagent otherwise employed.

A particle is defined as a small object that behaves as a whole unitwith respect to its transport and properties. The Bi₂S₃—CdS particles ofthe present disclosure in any of their embodiments may be in the form ofparticles of the same shape or different shapes, and of the same size ordifferent sizes. An average diameter (e.g., average particle size) ofthe particle, as used herein, refers to the average linear distancemeasured from one point on the particle through the center of theparticle to a point directly across from it. Microparticles areparticles having an average diameter between 0.1 and 100 μm in size.Nanoparticles are particles having an average diameter between 1 and 100nm in size.

A first aspect of the present disclosure relates to Bi₂S₃—CdS particlescomprising bismuth(III) sulfide, and cadmium(II) sulfide. Mostpreferably, the Bi₂S₃—CdS particles are in the form of spheres.Preferably, the Bi₂S₃—CdS particles may be substantially sphericalhaving oval or oblong shape. In one or more embodiments, the Bi₂S₃—CdSparticles of the present disclosure may be uniform. As used herein, theterm “uniform” refers to no more than 10%, preferably no more than 5%,preferably no more than 4%, preferably no more than 3%, preferably nomore than 2%, preferably no more than 1% of the distribution of theBi₂S₃—CdS particles having a different shape. For example, the Bi₂S₃—CdSparticles are uniform and have no more than 1% of the particles in asubstantially cylinder or rectangle shape. In certain embodiments, theBi₂S₃—CdS particles may be non-uniform. As used herein, the term“non-uniform” refers to more than 10% of the distribution of theBi₂S₃—CdS particles having a different shape. In certain embodiments,the Bi₂S₃—CdS particles may comprise additional shapes that providedesired photocatalytic and/or antimicrobial activity including, but notlimited to, a flake, a rod, a cylinder, a rectangle, a triangle, apentagon, a hexagon, a prism, a disk, a platelet, a cube, a cuboid, andan urchin (e.g. a globular particle possessing a spiky uneven surface).In one or more embodiments, the Bi₂S₃—CdS particles have an averagediameter of 0.3-5 μm, 0.4-4 μm, 0.5-3 μm, 0.6-2 μm, 0.7-1.5μm, or0.8-1μm. In a preferred embodiment, the Bi₂S₃—CdS particles are in theform of spheres having an average diameter of 0.3-5 μm, 0.4-4 μm, 0.5-3μm, 0.6-2 μm, 0.7-1.5 μm, or 0.8-1 μm.

As defined herein, “surface roughness” refers to a component of surfacetexture. It may be quantified by the deviations in the direction of thenormal vector of a real surface from its ideal form. In surfacemetrology, roughness is typically considered to be the high-frequency,short-wavelength component of the measured surface. In one embodiment,the Bi₂S₃—CdS particles of the present disclosure are in the form ofspheres having an uneven surface (see FIGS. 1A and 1B). The unevensurface may have an irregular contour that is bumpy, jagged, spiky,serrated, or zigzag. In a preferred embodiment, the Bi₂S₃—CdS particleshave a surface roughness in a range from 0.05-50 nm, 0.1-25 nm, 0.5-10nm, or 1-5 nm.

As used herein, “dispersity” is a measure of the heterogeneity of sizesof molecules or particles in a mixture. In probability theory orstatistics, the coefficient of variation (CV), also known as relativestandard deviation (RSD) is a standardized measure of dispersion of aprobability distribution. It is expressed as a percentage and may bedefined as the ratio of the standard deviation (σ) to the mean (μ, orits absolute value |μ∥). The coefficient of variation or relativestandard deviation is widely used to express precision and/orrepeatability. It may show the extent of variability in relation to themean of a population. In a preferred embodiment, the Bi₂S₃—CdS particlesof the present disclosure have a narrow size dispersion, i.e.monodispersity. As used herein, “monodisperse”, “monodispersed”, and/or“monodispersity” refers to Bi₂S₃—CdS particles which have a CV or RSD ofless than 30%, preferably less than 25%, preferably less than 20%,preferably less than 15%, preferably less than 12%, preferably less than10%, preferably less than 8%, preferably less than 5%.

The Brunauer-Emmet-Teller (BET) theory (S. Brunauer, P. H. Emmett, E.Teller, J. Am. Chem. Soc. 1938, 60, 309-319, incorporated herein byreference) aims to explain the physical adsorption of gas molecules on asolid surface and serves as the basis for an important analysistechnique for the measurement of a specific surface area of a material.Specific surface area is a property of solids which is the total surfacearea of a material per unit of mass, solid or bulk volume, or crosssectional area. In most embodiments, pore volume and BET surface areaare measured by gas adsorption analysis, preferably N₂ adsorptionanalysis. In one or more embodiments, the Bi₂S₃—CdS particles of thepresent disclosure have a BET surface area in a range of 1-50 m²/g,preferably 2-40 m²/g, preferably 4-30 m²/g, preferably 6-25 m²/g,preferably 8-20 m²/g, preferably 10-18 m²/g, preferably 11-16 m²/g,preferably 12-14 m²/g. In one or more embodiments, the Bi₂S₃—CdSparticles of the present disclosure have a pore volume of 0.02-0.4cm³/g, 0.03-0.2 cm³/g, 0.04-0.1 cm'/g, or 0.06-0.08 cm³/g.

The Bi₂S₃—CdS particles may be macroporous, mesoporous, or microporous.The term “microporous” means the pores of the particles have an averagepore size of less than 2 nm. The term “mesoporous” means the pores ofthe particles have an average pore size of 2-50 nm. The term“macroporous” means the pores of the particles have an average pore sizelarger than 50 nm. In one or more embodiments, the Bi₂S₃—CdS particlesare mesoporous, and have an average pore size in a range of 4-50 nm,6-40 nm, 8-30 nm, 10-25 nm, or 15-20 nm. In another embodiment, theBi₂S₃—CdS particles have an average pore size in a range of 51-100 nm,60-90 nm, or 70-80 nm.

As used herein, bismuth (III) sulfide (Bi₂S₃) is a chemical compound ofbismuth and sulfur. It occurs in nature as the mineral bismuthinite.Bismuth (III) sulfide can be prepared by reacting a bismuth (III) saltwith hydrogen sulfide and bismuth (III) sulfide can also be prepared bythe reaction of elemental bismuth and elemental sulfur in an evacuatedsilica tube at elevated temperatures (˜500° C.) for an extended periodof time (˜96 hours). Bismuth (III) sulfide is isostructural with Sb₂S₃.stibnite, consisting of linked ribbons. Bismuth atoms are in twodifferent environments, both of which have 7 coordinate bismuth atoms, 4in a near planar rectangle and three more distant making an irregular7-coordination group.

As used herein, cadmium(II) sulfide is the inorganic compound with theformula CdS. It occurs in nature with two different crystal structuresas the rare minerals greenockite and hawleyite. As a compound that iseasy to isolate and purify, cadmium(II) sulfide is the principal sourceof cadmium for commercial applications. Cadmium(II) sulfide can beprepared by the precipitation from soluble cadmium(II) salts withsulfide ions. Cadmium(II) sulfide has two crystal forms. The more stablehexagonal wurtzite structure (found in the mineral Greenockite) and thecubic zinc blende structure (found in the mineral Hawleyite). In both ofthese forms the cadmium and sulfur atoms are tetra-coordinated.

In a preferred embodiment, the Bi₂S₃—CdS particles have an atomic ratioof bismuth to cadmium in a range of 0.5:1 to 4:1, preferably 0.75:1 to3.5:1, preferably 1:1 to 3:1, preferably 1.25:1 to 2.5:1, preferably1.5:1 to 2.25:1, or about 2:1. In a preferred embodiment, the Bi₂S₃—CdSparticles have an atomic ratio of sulfur to bismuth in a range of 3:2 to8:1, preferably 1.6:1 to 6:1, preferably 1.7:1 to 4:1, preferably 1.75:1to 3:1, or about 2:1. In a preferred embodiment, the Bi₂S₃—CdS particleshave an atomic ratio of sulfur to cadmium in a range of 2:1 to16:1,preferably 2.5:1 to 12:1, preferably 3:1 to 8:1, preferably 3.5:1 to6:1, or about 4:1. In a preferred embodiment, the Bi₂S₃—CdS particleshave a molar ratio of bismuth (III) sulfide to cadmium(II) sulfide in arange of 1:8 to 8:1, preferably 1:6 to 6:1, preferably 1:5 to 5:1,preferably 1:4 to 4:1, preferably 1:3 to 3:1, preferably 1:2 topreferably 1:1.2 to 1.2:1, or about 1:1.

In certain embodiments, the bismuth (III) sulfide (Bi₂S₃) and thecadmium(II) sulfide (CdS) may be homogeneously dispersed to &ilia theBi₂S₃—CdS particles. In certain embodiments, the Bi₂S₃ and CdS may formone or more layers of each other throughout the Bi₂S₃—CdS particles. Incertain embodiments, the Bi₂S₃ may form a shell around a core of CdS inthe Bi₂S₃—CdS particles. Alternatively, the CdS may form a shell arounda core of Bi₂S₃ in the Bi₂S₃—CdS particles. In a preferred embodiment,the Bi₃S₃ is affixed to one or more surfaces of the CdS in the Bi₂S₃—CdSparticles. These materials may be affixed in any reasonable manner, suchas physisorption or chemisorption and mixtures thereof via strong atomicbonds (e.g. ionic, metallic, and covalent bonds) and/or weakinteractions such as van der Waals, or hydrogen bonds. In certainembodiments, the Bi₂S₃—CdS particles comprise Bi₂S₃ and/or CdSincorporated into the lattice structure of the CdS and/or Bi₂S₃. Forexample, the elemental Bi₂S₃ may be embedded, between CdS molecules tobecome integral with the lattice. Alternatively, the Bi₂S₃ may beembedded into the pores of the CdS lattice and thus not integral to theCdS lattice. In certain alternative embodiments, the Bi₂S₃ and/or CdS isnot incorporated into the lattice structure of CdS and/or Bi₂S₃ and maybe adsorbed on the surface (e.g. by van der Waals and/or electrostaticforces) of the CdS and/or Bi₂S₃.

Another aspect of the present disclosure relates to a method ofpreparing the Bi₂S₃—CdS particles. The method involves (i) mixing abismuth(III) salt, a cadmium(II) salt, and an optionally substitutedthiourea in a solvent in the presence of polyvinylpyrrolidone to form areaction mixture, and (ii) heating the reaction mixture in an autoclaveat a temperature of 100-300° C. for 2-48 hours, thereby forming theBi₂S₃—CdS particles.

As used herein, the term “solvent” includes, but is not limited to,water (e.g. tap water, distilled water, deionized water, deionizeddistilled water), organic solvents, such as ethers (e.g. diethyl ether,tetrahydrofuran, 1,4-dioxane, tetrahydropyran, t-butyl methyl ether,cyclopentyl methyl ether, di-iso-propyl ether), glycol ethers (e.g.1,2-dimethoxyethane, diglymer, triglyme), alcohols (e.g. methanol,ethanol, trifluoroethanol, n-propanol, propanol, n-butanol, i-butanol,t-butanol, n-pentanol, i-pentanol, 2-methyl-2-butanol,2-trifluoromethyl-2-propanol, 2,3-dimethyl-2-butanol, 3-pentanol,3-methyl-3-pentanol, 2-methyl-3-pentanol, 2-methyl-2-pentanol,2,3-dimethyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol,3-hexanol, cyclopropylmethanol, cyclopropanol, cyclobutanol,cyclopentanol, cyclohexanol), aromatic solvents (e.g. benzene, o-xylene,m-xylene, p-xylene, mixtures of xylenes, toluene, mesitylene, anisole,1,2-dimethoxybenzene, α,α,α-trifluoromethylbenzene, fluorobenzene),chlorinated solvents (e.g. chlorobenzene, dichloromethane,1,2-dichloroethane, 1,1-dichloroethane, chloroform), ester solvents(e.g. ethyl acetate, propyl acetate), urea solvents, ketones (e.g.acetone, butanone), acetonitrile, propionitrile, butyronitrile,benzonitrile, dimethyl sulfoxide, ethylene carbonate, propylenecarbonate, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, andmixtures thereof. As used herein solvent may refer to non-polar solvents(e.g. hexane, benzene, toluene, diethyl ether, chloroform, 1,4-dioxane),polar aprotic solvents (e.g. ethyl acetate, tetrahydrofuran,dichloromethane, acetone, acetonitrile, dimethylformamide, dimethylsulfoxide), and polar protic solvents (e.g. acetic acid, n-butanol,isopropanol, n-propanol, ethanol, methanol, ethylene glycol, diethyleneglycol, triethylene glycol, formic acid, water), and mixtures thereof.In a preferred embodiment, the solvent used herein is a polar proticsolvent, preferably a diol (e.g. ethylene glycol, diethylene glycol,triethylene glycol). Most preferably the solvent is ethylene glycol.

As used herein, a salt refers to an ionic compound resulting from theneutralization reaction of an acid and a base. Salts are composed ofrelated numbers of cation (positively charged ions) and anions(negatively charged ions) such that the product is electrically neutral(without a net charge). These component ions may be inorganic (e.g.chloride, Cl⁻) or organic (e.g. acetate, CH₃CO₂ ⁻) and may be monoatomic(e.g. fluoride, F⁻) or polyatomic (e.g. sulfate, SO₄ ²⁻). Exemplaryconventional salts include, but are not limited to, those derived frominorganic acids including, but not limited to, hydrochloric,hydrobromic, sulfuric, sulfamic, phosphoric, and nitric; and thosederived from organic acids including, but not limited to, acetic,propionic, succinic, glycolic, stearic, lactic, malic, tartaric, citric,ascorbic, pamoic, maleic, hydroxymaleic, phenylacetic, glutamic,benzoic, salicyclic, sulfanilic, 2-acetoxybenzoic, fumaric,toluenesulfonic, methanesulfonic, ethane disulfonic, oxalic, isethionic,and mixtures and hydrates thereof and the like. The present disclosureincludes all hydration states of a given salt or formula, unlessotherwise noted. For example, Bi(NO₃)₃ includes anhydrous Bi(NO₃)₃,pentahydrate Bi(NO₃)₃.5H₂O, and any other hydrated forms or mixtures.Cd(NO₃)₂ includes anhydrous Cd(NO₃)₂, tetrahydrate Cd(NO₃)₂.4H₂O, andany other hydrated forms or mixtures.

In one or more embodiments, an atomic ratio of bismuth to cadmium in thereaction mixture is in a range of 0.5:1 to 4:1, preferably 1:1 to 3.5:1,preferably 1.5:1 to 3:1, or about 2:1. However, in certain embodiments,the atomic ratio of bismuth to cadmium in the reaction mixture may beless than 0.5:1 or greater than 4:1.

Exemplary suitable bismuth(III) salts include, but are not limited to,bismuth(III) nitrate, bismuth (iii) nitrate pentahydrate, bismuth (III)bromide, bismuth (III) chloride, bismuth (III) fluoride, bismuth (III)iodide, bismuth (III) oxychloride. In a preferred embodiment, thebismuth(III) salt is bismuth(III) nitrate, Bi(NO₃)₃, bismuth(III)nitrate pentahydrate Bi(NO₃)₃.5H₂O, or a mixture thereof. In one or moreembodiments, when present, the concentration of the bismuth nitrate inthe reaction mixture is in a range of 1-1,000 mM, preferably 5-750 mM,preferably 10-500 mM, preferably 15-250 mM, preferably 20-100 mM, orabout 25 mM.

Exemplary suitable cadmium(II) salts include, but are not limited to,cadmium(II) nitrate, cadmium(II) nitrate tetrahydrate, cadmium(II)chloride, cadmium(II) bromide, cadmium(II) iodide, cadmium(II) acetate,and cadmium(II) carbonate. In a preferred embodiment, the cadmium(II)salt is cadmium(II) nitrate, cadmium(II) nitrate tetrahydrate,Cd(NO₃)₂.4H₂O, or a mixture thereof. In one or more embodiments, whenpresent, the concentration of cadmium(II) nitrate in the reactionmixture is in a range of 2-2,000 mM, preferably 10-1,500 mM, preferably20-1,000 mM, preferably 30-500 mM, preferably 40-200 mM, or about 50 mM.

As used herein, an optionally substituted thiourea refers to a broadclass of compounds with the general structure (R¹R²N)(R³R⁴N)C═S whereinR¹, R², R³, and R⁴ are each independently a hydrogen, an optionallysubstituted alkyl, an optionally substituted cycloalkyl, an optionallysubstituted cycloalkylalkyl, an optionally substituted arylalkyl, anoptionally substituted alkenyl, an optionally substituted heteroaryl, anoptionally substituted aryl, an optionally substituted heterocyclyl, anoptionally substituted aryl olefin, or an optionally substituted vinyl.As used herein, the term “substituted” refers to at least one hydrogenatom that is replaced with a non-hydrogen group, provided that normalvalencies are maintained and that the substitution results in a stablecompound.

Exemplary suitable optionally substituted thiourea compounds include,but are not limited to, thiourea (NH₂CSNH₂), 1,3-diisopropyl-2-thiourea,1,3-di-p-tolyl-2-thiourea, 1-(2-methoxyphenyl)-2-thiourea, propylenethiourea, 1-(4-nitrophenyl)-2-thiourea, 1-(3-nitrophenyl)-2-thiourea,N-Boc-thiourea, (2,3-difluorophenyl)thiourea,(3,5-dimethylphenyl)thiourea, (4-cyanophenyl)thiourea,(4-fluorophenyl)thiourea, 1-(3-carboxyphenyl)-2-thiourea,(2,5-difluorophenyl)thiourea, (3-fluorophenyl)thiourea,(2,4-difluorophenyl)thiourea, (2,6-difluorophenyl)thiourea,(2-fluorophenyl)thiourea, (4-acetylphenyl)thiourea,1-(2,3-dichlorophenyl)-2-thiourea, 1-(2-bromophenyl)-2-thiourea,1-(2-ethylphenyl)-2-thiourea, 1-(2-furfuryl)-2-thiourea,1-(2-tetrahydrofurfuryl)-2-thiourea,1-(3,4-methylenedioxyphenyl)-2-thiourea, 1-(3-acetylphenyl)-2-thiourea,1-(3-bromophenyl)-2-thiourea, 1-(3-cyanophenyl)-2-thiourea,1-(3-ethoxycarbonylphenyl)-2-thiourea, 1-(3-methoxybenzyl)-2-thiourea,1-(3-phenylpropyl)-2-thiourea, 1-(4-chlorophenyl)-2-thiourea,1-(4-ethoxycarbonylphenyl)-2-thiourea,N-(2,4,6-trichlorophenyl)thiourea, N-(3,5-dichlorophenyl)thiourea,N-(4-phenoxyphenyl)thiourea, N-(4-pyridyl)thiourea,N-(6-quinolinyl)thiourea, N-(8-quinolinyl)thiourea,N,N′-di-Boc-thiourea, [3-(trifluoromethyl)phenyl]thiourea,1-cyclohexyl-3-(2-morpholinoethyl)-2-thiourea,[4-(trifluoromethyl)phenyl]thiourea,1,3-bis[3,5-bis(trifluoromethyl)phenyl]thiourea,1-[4-(dimethylamino)phenyl]-2-thiourea,1-(1,3-diphenyl-1H-pyrazol-5-yl)thiourea,1-(3-chloro-4-fluorophenyl)thiourea,1-(4-(4-bromophenoxy)phenyl)thiourea,1-(4-(4-chlorophenoxy)phenyl)thiourea,1-(4-(4-fluorophenoxy)phenyl)thiourea,1-(4-(4-methoxyphenoxy)phenyl)thiourea, 1-(4(p-tolyloxy)phenyl)thiourea,1-(4-chlorophenyl-3-[2-phenylacetyl)amino]thiourea,1-(5-chloro-2-(trifluoromethyl)phenyl)thiourea,1-benzyl-3-(2,6-dimethylphenyl)thiourea,1-benzyl-3-(2-ethoxyphenyl)thiourea,1-benzyl-3-(4-methoxyphenyl)thiourea,1-benzyl-3-(naphthalen-1-yl)thiourea,1-ethyl-3-(2-methoxyphenyl)thiourea, 1-ethyl-3-(4-fluorophenyl)thiourea,[4-bromo-2-(trifluoromethyl)phenyl]thiourea,N-[2-(trifluoromethyl)phenyl]thiourea,N-(1,3-dimethyl-1H-pyrazol-5-yl)thiourea,N-(1H-1,3-benzimidazol-5-yl)thiourea, N-(1H-indazol-5-yl)thiourea,N-(1H-indazol-6-yl)thiourea, N-(1H-indazol-7-yl)thiourea,N-phenylthiourea, N-(1-naphthyl)thiourea, N-allylthiourea,N,N′-diphenylthiourea, 1,1,3-triphenyl-2-thiourea,1,3-di-tert-butyl-2-thiourea, 1,3-diallyl-2-thiourea,1,3-dibenzyl-2-thiourea, 1,3-dicyclohexyl-2-thiourea,1,3-difurfuryl-2-thiourea, 1,3-diheptyl-2-thiourea,1,3-dihexadecyl-2-thiourea, 1,3-dihexyl-2-thiourea,1,3-dioctyl-2-thiourea, 1,3-dipropyl-2-thiourea,1-(2,4,6-tribromophenyl)-2-thiourea, 1-(2,4-dichlorophenyl)-2-thiourea,1-(2,6-xylyl-2-thiourea, 1-(3,4-dimethoxyphenyl)-2-thiourea,1-(3-chlorophenyl)-2-thiourea, 1-(3-methoxypropyl)-2-thiourea,1-benzyl-2-thiourea, 1-butyl-2-thiourea, 1-dodecanoyl-2-thiourea,N-(2,4-dimethylphenyl)thiourea, N-(2,5-dichlorophenyl)thiourea,N-(2,6-dichlorophenyl)thiourea, N-(2-phenylethyl)thiourea,N-(3,4-dichlorophenyl)thiourea, N-(3,4-dimethylphenyl)thiourea,N-(3-methoxyphenyl)thiourea, N-(4-bromophenyl)thiourea,N-(4-chlorophenyl)thiourea, N-(4-ethoxyphenyl)thiourea,N-(4-ethylphenyl)thiourea, N-(4-methoxyphenyl)thiourea,N-(4-methylphenyl)thiourea, N-(tert-butyl)thiourea,(2,3-dimethyl-phenyl)thiourea, (2,4,6-trimethyl-phenyl)thiourea,(3,4,5-trimethoxy-phenyl)thiourea, (4-ethoxy-phenyl)thiourea,(phenyl-phenylimino-methyl)thiourea, and the like.

In a preferred embodiment, the optionally substituted thiourea isthiourea of formula SC(NH₂)₂, where R¹═R²═R³═R⁴═—H. Thiourea is anorganosulfur compound that is structurally similar to urea, except thatthe oxygen atom is replaced by a sulfur atom, but the properties of ureaand thiourea differ. Thiourea is a reagent in organic synthesis, whichis commonly employed as a source of sulfide, often with reactionsproceeding via the intermediacy of isothiuronium salts with the reactioncapitalizing on the high nucleophilicity of the sulfur center and easyhydrolysis of the intermediate isothiouronium salt.

In one or more embodiments, the concentration of the optionallysubstituted thiourea in the reaction mixture is in a range of 0.01-1 M,preferably 0.05-0.75 M, preferably 0.1-0.5 M, preferably 0.15-0.25 M. Ina preferred embodiment, a molar ratio of the optionally substitutedthiourea to the bismuth(III) salt is in a range of 2:1 to 10:1,preferably 3:1 to 9:1, preferably 4:1 to 8:1, preferably 5:1 to 7:1, orabout 6:1. In a preferred embodiment, the molar ratio of the optionallysubstituted thiourea to the cadmium(II) salt is in a range of 1:2 to6:1, preferably 1:1 to 5:1, preferably 2:1 to 4:1, or about 3:1.

As used herein, polyvinylpyrrolidone (PVP), also commonly known aspolyvidone or povidone, refers to a water soluble polymer obtainablefrom the monomer N-vinylpyrrolidone. In certain embodiments polyvinylpyrrolidone may refer to cross-linked derivatives, a highly cross-linkedmodification of polyvinyl pyrrolidone (PVP) known aspolyvinylpolypyrrolidone (PVPP, crospovidone, crospolividone, or E1202).PVP binds to polar molecules exceptionally well, owing to its polarity.PVP is soluble in water and other polar solvents including alcohols(e.g. methanol and ethanol) as well as more exotic solvents (e.g. deepeutectic solvent and urea). In solution, PVP has excellent wettingproperties and readily forms films.

PVP polymers are available in several viscosity grades, ranging from lowto high molecular weight and may be supplied in various viscosity gradesas a powder and/or aqueous solution. Exemplary suitable commercialgrades of polyvinylpyrrolidone include, but are not limited to, PVPK-12, PVP K-15, PVP K-30, PVP K-60, PVP K-90, and PVP K-120. The K-valueassigned to various grades of PVP polymer may represent a function ofthe average molecular weight, the degree of polymerization, and theintrinsic viscosity. The K-values may be derived from viscositymeasurements and calculated according to Fikentscher's formula. In apreferred embodiment, the polyvinyl pyrrolidone has a K-value in a rangeof 8-140, preferably 10-100, preferably 15-80, preferably 20-60,preferably 25-40.

Some of the techniques for measuring the molecular weight of various PVPpolymer products are based on measuring sedimentation, light scattering,osmometry, NMR spectroscopy, ebullimometry, and size exclusionchromatography for determining absolute molecular weight distribution.By the use of these methods, any one of three molecular weightparameters can be measured, namely the number average (Mn), viscosityaverage (Mv), and weight average (Mw) molecular weights. As used herein,the mass average molar mass or weight average molar mass (Mw) describesthe molar mass of a polymer with some properties dependent on molecularsize, so a larger molecule will have a larger contribution than asmaller molecule. In some embodiments, the polyvinylpyrrolidone usedherein has a weight average molar mass (Mw) in a range of 10,000-400,000g/mol, preferably 12,000-360,000 g/mol, preferably 15,000-300,000 g/mol,preferably 20,000-200,000 g/mol, preferably 30,000-100,000 g/mol,preferably 40,000-90,000 g/mol, preferably 50,000-80,000 g/mol,preferably 60,000-70,000 g/mol.

As used herein, the polydispersity index (PDI or heterogeneity index) isa measure of the distribution of molecular mass in a given polymersample. The PDI is calculated as the weight average molecular weightdivided by the number average molecular weight. Typically, dispersitiesvary based on the mechanism of polymerization and can be affected by avariety of reaction conditions such as reactant ratios, how close thepolymerization went to completion, etc. In one embodiment, thepolyvinylpyrrolidone used herein has a PDI of up to 6, preferably up to5, preferably up to 3, preferably up to 2.5, preferably up to 2,preferably up to 1.5, preferably up to 1.25. As used herein, a degree ofpolymerization (DP) is defined as the number of monomeric units in amacromolecule or polymer. In one embodiment, the polyvinylpyrollidoneused herein has a degree of polymerization of 50-5000, preferably100-2500, preferably 100-1500, preferably 100-750, preferably 100-300.

In a preferred embodiment, 1-40 g of polyvinylpyrrolidone is present perliter of the reaction mixture, preferably 5-35 g/L, preferably 10-30g/L, preferably 15-25 g/L, preferably 18-22 g/L, or about 20 g ofpolyvinylpyrrolidone is present per liter of the reaction mixture.

In one or more embodiments, the reaction mixture is heated at atemperature of 100-300° C., preferably 120-280° C., preferably 140-260°C., preferably 160-240° C., preferably 175-225° C., preferably 180-220°C. In a preferred embodiment, the reaction mixture is heated at atemperature of 180-220° C., preferably 182-218° C., preferably 184-216°C., preferably 186-214° C., preferably 188-212° C., preferably 190-210°C., preferably 192-208° C., preferably 194-206° C., preferably 196-204°C., preferably 198-202° C., or about 200° C. In one or more embodiments,the reaction mixture is heated for a time period of 1-60 hours,preferably 2-48 hours, preferably 4-44 hours, preferably 8-40 hours,preferably 10-36 hours, preferably 12-32 hours, preferably 16-28 hours.In a preferred embodiment, the reaction mixture is heated for a timeperiod of 16-28 hours, preferably 17-27 hours, preferably 18-26 hours,preferably 19-25 hours, preferably 19.5-24.5 hours, or about 24 hours.In certain embodiments, the reaction mixture may be stirred (e.g. at aspeed of 50-1000 rpm, 50-900 rpm, 50-700 rpm, 50-500 rpm, 100-500 rpm,or 200-400 rpm), or in certain embodiments the reaction mixture may beleft to stand or not agitated during the heating.

The heating may be preferably conducted in an autoclave, more preferablya Teflon lined autoclave. After heating, the autoclave may be left tocool to a temperature in a range of 10-40° C., preferably 10-30° C.,preferably 20-30° C. The Bi₂S₃—CdS particles may becollected/washed/dried by methods commonly known to those of ordinaryskill in the art. For example, the Bi₂S₃—CdS particles may be collectedby filtering and/or centrifugation, washed one or more times withsolvents such as water and ethanol and dried in an oven or ambientconditions at a temperature in a range of 40-100° C., preferably 45-90°C., preferably 50-80° C., preferably 55-70° C. for a time period of 1-48hours, preferably 6-36 hours, preferably 10-30 hours, preferably 20-28hours, preferably 22-26 hours.

Another aspect of the present disclosure relates to method for degradingan organic pollutant using Bi₂S₃—CdS particles. Preferably, theseBi₂S₃—CdS particles comprise bismuth(III) sulfide and cadmium(II)sulfide, and are in the form of spheres, with composition ratios, andstructural dimensions as described previously. The Bi₂S₃—CdS particlesmay have similar properties as described for those in the first aspect,such as average particle diameter, surface area, pore size, pore volume,and/or some other property. In preferred embodiments, the Bi₂S₃—CdSparticles used herein for degrading the organic pollutant haveaforementioned atomic ratios of bismuth to cadmium, sulfur to bismuth,and sulfur to cadmium, shapes, average diameters, BET surface areas,pore volumes, and average pore sizes.

The method for degrading an organic pollutant using Bi₂S₃—CdS particlesinvolves (i) contacting the Bi₂S₃—CdS particles with an aqueous solutioncomprising the organic pollutant to form a mixture, and (ii)illuminating the mixture with a light at a wavelength in a range of200-700 nm, 250-600 nm, 300-500 nm, or 320-400 nm for 0.1-6 hours, 0.5-5hours, 1-4 hours, or 2-3 hours, thereby degrading the organic pollutant.As used herein, the term degrading or “degradation” refers to breakingdown the organic pollutant into atoms, ions, and/or smaller molecularfractions (e.g., nitrogen gas, carbon dioxide, water). Degradation of anorganic pollutant involves breaking existing chemical bonds in themolecular structure of the organic pollutant so as to change thephysical, chemical, and/or biological properties of the organicpollutant.

In one or more embodiments, an amount of the Bi₂S₃—CdS particles in themixture is in a range of 0.1-10 g/L, 0.2-9 g/L, 0.3-8 g/L, 0.4-7 g/L,0.5-6 g/L, 0.6-5 g/L, 0.7-4 g/L, 0.8-3 g/L, 0.9-2 g/L, or about 1 g/Lrelative to a total volume of the mixture. In certain embodiments, theBi₂S₃—CdS particles are dispersed within the mixture, and may further befiltered and/or recycled after the degradation. In one or moreembodiments, before degrading occurs, the organic pollutant may bepresent in the aqueous solution at a concentration of 1-1,000 mg/L,2-750 mg/L, 4-500 mg/L, 6-250 mg/L, 8-100 mg/L, 9-50 mg/L, or 10-25 mg/Lrelative to a total volume of the aqueous solution. Water present in theaqueous solution may be tap water, distilled water, doubly distilledwater, deionized water, deionized distilled water, reverse osmosiswater, or combinations thereof. Non-limiting examples of aqueoussolutions (i.e. organic pollutants contaminated aqueous solutions),water sources and systems include surface water that collects on theground or in a stream, aquifer, river, lake, reservoir or ocean, groundwater that is obtained by drilling wells, run-off, industrial water,industrial textile wastewater, public water storage towers, publicrecreational pools and/or bottled water.

The method may be carried out in tanks, containers, or small scaleapplications in both batch mode and continuous process. To limit orprevent evaporation, the mixture may be in a sealed vessel or some othercontainer, preferably with a transparent window. The vessel may compriseglass, quartz, or a polymeric material transparent to ultraviolet lightand chemically stable with the mixture. As defined herein, “transparent”refers to an optical quality of a compound wherein a certain wavelengthor range of wavelengths of light may traverse through a portion of thecompound with a small loss of light intensity. A material that causes aloss of less than 25%, preferably less than 20%, preferably less than10%, preferably less than 5%, preferably less than 2% of the intensityof a certain wavelength or range of wavelengths of light may beconsidered transparent.

The illumination sourcemay be any known light source including, but notlimited to, natural solar sunlight, UV light, laser light, incandescentlight, and the like. Exemplary light sources include, but are notlimited to, a xenon lamp, a mercurial lamp, a metal halide lamp, an LEDlamp, a solar simulator, and a halogen lamp. Preferably the light sourceis a xenon lamp including, but not limited to, a xenon arc lamp or axenon flash lamp. Two or more light sources nay be used. In certainembodiments, sunlight may be used as the light source. In a preferredembodiment, the mixture is illuminated with light having a wavelength of200-700 nm, 250-600 nm, 300-500 nm, or 320-400 nm. The illuminationsource may have a total power output of 50-1,000 W, preferably 100-750W, more preferably 200-500 W, and may be positioned 1-50 cm, 5-40 cm,10-30 cm, or 15-20 cm from the closest surface of the mixture. Themixture may be illuminated for a time period of 5-720 minutes,preferably 15-600 minutes, preferably 30-480 minutes, preferably 45-360minutes, preferably 60-240 minutes, preferably 90-180 minutes.

The mixture may be shaken, stirred, or agitated throughout the durationof the degradation by employing a rotary shake, a magnetic stirrer, oran overhead stirrer. In another embodiment, the mixture is left to stand(i.e. not agitated). In one embodiment, the mixture is sonicated. Thedegradation may be performed at a temperature in a range of 10-70° C.,12-60° C., 15-50° C., 18-40 20-35° C., or 25-30° C. The mixture may betemperature regulated to prevent overheating and/or evaporation, forexample, via a water tubing, a water and/or ice bath, ice packs, or aircooling. In one embodiment, the degradation method is performed at apressure in a range of 0.5-2 atm, 0.7-1.8 atm, 0.8-1.5 atm, orpreferably 0.9-1.2 atm.

The Bi₂S₃—CdS particles may be used to photodegrade organic dyes.Exemplary organic dyes that may be degraded by the method disclosedherein using the Bi₂S₃—CdS particles include, but are not limited to,methyl green, methylene blue, malachite green, brilliant green,brilliant blue FCF, new methylene blue, methyl blue, methyl purple,thymol blue, rhodamine B, methyl violet 2B, methyl violet 6B, crystalviolet, phenol red, acid green 5, basic fuchsin, acid fuchsin, patentblue V, pararosaniline, Victoria blue B, Victoria blue FBR, Victoriablue BO, Victoria blue FGA, Victoria blue 4 R, Victoria blue R, and azodyes such as methyl orange, methyl red, methyl yellow, Congo red, directblue 1, basic red 18, direct brown 78, trypan blue, disperse orange 1,alizarine yellow R, Sudan III, Sudan IV, Sudan black B, and orange G. Inat least one embodiment, the organic pollutant comprises methyl orange,methyl green, or both. The method disclosed herein may degrade one ormore organic dyes present as the organic pollutant in the mixture.

Other organic pollutants that may be degraded by the method disclosedherein using the Bi₂S₃—CdS particles include, but are not limited to,organic pesticides such as aldrin, chlordane, DDT, dieldrin, endrin,heptachlor, hexachlorobenzene, mirex, and toxaphene, herbicides such asglyphosate, 2-methyl-4-chloropherioxyacetic acid,2,4-dichlorophenoxyacetic acid, and 2,4,5-trichloropherioxyacetic acid,industrial chemicals such as hexachlorobenzene, polychlorinatedbiphenyls (PCBs), and methyl tertiary butyl ether.

The reduction in the concentration of the organic pollutants in themixture may be monitored by UV-vis spectroscopy (see FIGS. 4 and 5),high-pressure liquid chromatography (HPLC), liquid chromatography-massspectrometry (LC-MS), and nuclear magnetic resonance (NMR) spectroscopy.In one or more embodiments, at least 10%, at least 20%, at least 25%, orat least 30% by mole of the organic pollutant in the mixture is degradedwithin 5 minutes, within 10 minutes, within 15 minutes, within 30minutes, within 45 minutes, within 60 minutes, within 75 minutes, within90 minutes, within 105 minutes, or within 120 minutes of illuminating.In one embodiment, when methyl green is present as the organicpollutant, at least 50%, at least 60%, at least 70%, at least 80%, atleast 90%, at least 95%, or at least 98% by mole of the methyl green isdegraded within 30 minutes, within 45 minutes, within 60 minutes, within75 minutes, within 90 minutes, within 105 minutes, or within 120 minutesof illuminating (see FIGS. 4 and 6). In another embodiment, when methylorange is present as the organic pollutant, at least 20%, at least 25%,at least 30%, at least 35%, or at least 40% by mole of the methyl orangeis degraded within 30 minutes, within 45 minutes, within 60 minutes,within 75 minutes, within 90 minutes, within 105 minutes, or within 120minutes of illuminating (see FIGS. 5 and 6).

Another aspect of the present disclosure relates to a method forpreventing or reducing growth of a microorganism on a surface usingBi₂S₃—CdS particles. Preferably, these Bi₂S₃—CdS particles comprisebismuth(III) sulfide and cadmium(II) sulfide, and are in the form ofspheres, with composition ratios and structural dimensions as describedpreviously. The Bi₂S₃—CdS particles may have similar properties asdescribed for those in the first aspect, such as average particlediameter, surface area, pore size, pore volume, and/or some otherproperty. In preferred embodiments, the Bi₂S₃—CdS particles used hereinfor preventing or reducing growth of a microorganism on a surface haveaforementioned atomic ratios of bismuth to cadmium, sulfur to bismuth,and sulfur to cadmium, shapes, average diameters, BET surface areas,pore volumes and average pore sizes.

In other embodiments, the Bi₂S₃—CdS particles having one or moredissimilar properties as compared to those described in the first aspectmay be used herein for preventing or reducing growth of a microorganismon a surface. For example, Bi₂S₃—CdS particles may be used which have anaverage diameter smaller than 0.3μm or greater than 5 μm. Alternatively,Bi₂S₃—CdS particles may be used which have a BET surface area smallerthan 1 m²/g or greater than 50 m²/g, a pore volume smaller than 0.02cm³/g or greater than 0.4 cm³/g, and/or an average pore size smallerthan 4 nm or greater than 50 nm. These Bi₂S₃—CdS particles withdissimilar properties may be prepared by using starting materials, suchas bismuth(III) salt, cadmium(II) salt, or optionally substitutedthiourea, that are at different concentrations than those describedpreviously. Alternatively, these Bi₂S₃—CdS particles with dissimilarproperties may be formed by changing the aforementioned reactionconditions, such as reaction time, and/or temperature.

The method for preventing or reducing growth of a microorganism on asurface using Bi₂S₃—CdS particles involves applying the Bi₂S₃—CdSparticles onto the surface. Preferably, the Bi₂S₃—CdS particles are incontact with the surface for 0.5-48 hours, 1-24 hours, 2-12 hours, or3-6 hours.

In one or inure embodiments, the Bi₂S₃—CdS particles are applied ontothe surface as a mixture (e.g. a solution, a suspension) comprising theBi₂S₃—CdS particles. Preferably, the Bi₂S₃—CdS particles are appliedonto the surface as a solution comprising a solvent and the Bi₂S₃—CdSparticles. The solution may comprise 1 μg/mL to 50 mg/mL of theBi₂S₃—CdS particles relative to a total volume of the solution,preferably 2 μg/mL to 40 mg/mL, preferably 4 μg/mL to 30 mg/mL,preferably 6 μg/mL to 20 mg/mL, preferably 8 μg/mL to 10 mg/mL,preferably 10 μg/mL to 8 mg/mL, preferably 50 μg/mL to 6 mg/mL,preferably 100 μg/mL to 4 mg/mL, preferably 200 μg/mL to 3 mg/mL,preferably 300 mg/mL, to 2 mg/mL, preferably 400 μg/mL to 1.5 mg/mL,preferably 500 μg/mL to 1 mg/mL. In one or more embodiments, the solventcomprises dimethyl sulfoxide (DMSO), water, or both. Preferably, thesolvent comprises DMSO and water and DMSO is present at a volumeconcentration of 0.1-10 vol %, 0.5-9 vol %, 1-8 vol %, 2-7 vol %, 3-6vol %, or 4-5 vol % relative to a total volume of the solvent. Thesolution may further comprise other compatible solvents such as ethanol,and isopropyl alcohol.

As used herein, “microoraanism” or “microbe” refers to in particularfungi, and gram-positive and gram-negative bacteria. The term“antimicrobial product” refers to a product demonstrating the capabilityto inhibit or prevent the proliferation of microorganisms. Gram-negativebacteria are bacteria that do not retain the crystal violet stain usedin the gram-staining method of bacterial differentiation.

In one or more embodiments, the Bi₂S₃—CdS particles are applied onto thesurface as an antimicrobial product containing the Bi₂S₃—CdS particlesat an amount of 0.01-99 wt %, 0.5-95 wt %, 1-90 wt %, 2-80 wt %, 5-70 wt%, 10-60 wt %, 20-50 wt %, 30-40 wt % relative to a total weight of theantibacterial product.

Exemplary antimicrobial products include, but are not limited to,antimicrobial coatings, hand sanitizer (including rinse off and leave-onand aqueous-based hand disinfectants), preoperative skin disinfectant,bar soap, liquid soap (e.g., hand soap), hospital disinfectants,disinfecting spray solution, household cleansing wipes, surfacesanitizer, personal care disinfecting wipes, body wash, acne treatmentproducts, antibacterial diaper rash cream, antibacterial skin cream,deodorant, antimicrobial creams, topical cream, a wound care item, suchas wound healing ointments, creams, and lotions.

The method disclosed herein may be used to prevent or reduce growth of amicroorganism on the skin of a subject. In a preferred embodiment, theBi₂S₃—CdS particles are applied onto the skin of a subject as anantimicrobial cream comprising 0.01-50 wt %, 0.1-40 wt %, 1-30 wt %,2-20 wt %, 4-15 wt %, or 5-10 wt % of the Bi₂S₃—CdS particles relativeto a total weight of the antimicrobial cream. The subject may be amammal, such as a human; a non-human primate, such as a chimpanzee, andother apes and monkey species; a farm animal, such as a cow, a horse, asheep, a goat, and a pig; a domestic animal, such as a rabbit, a dog,and a cat; a laboratory animal including a rodent, such as a rat, amouse, and a guinea pig, and the like. The antimicrobial cream mayfurther comprise other formulating components such as occlusioncomponents (e.g. petrolatum), film forming agents (e.g.polyvinylpyrrolidone), thickening agents (e.g. xanthan gum,polyacrylamide polymers), and/or emulsifiers (e.g. fatty acids, fattyalcohols). The formulation techniques of topical creams are generallyknown to those skilled in the art.

The method disclosed herein may also be used to prevent or reduce growthof a microorganism on the surface of an artificial restoration ormedical device. Exemplary artificial restorations include, withoutlimitation, dental restorations, dentures, dental prosthesis,craniofacial implants, artificial joints, and artificial bones.Exemplary medical devices include, but are not limited to, catheters,medical diagnosis instruments such as endoscopes, contact lenses,spectacles, hearing aids, and mouth guards.

Other surfaces suitable for the method disclosed herein include bothhard and soft surfaces. The term “hard surface” includes, but is notlimited to, bathroom surfaces (tub and tile, fixtures, ceramics),kitchen surfaces, countertops, appliances, flooring, glass, automobiles,and the like. “Soft surfaces” include but are not limited to fabrics,leather, carpets, furniture, upholstery and other suitable softsurfaces. The presently disclosed method may be particularly viable forsanitizing surfaces related to hospital and nursing care facilities andequipment such as hospital room, toilet, beds, sheets, pillows,wheelchairs, and canes.

The Bi₂S₃—CdS particles may be applied onto a desired area of thesurface as needed. In certain embodiments, the method disclosed hereininvolves applying the Bi₂S₃—CdS particles onto the surface 1 to 10 timesdaily, preferably 2 to 7 times daily, preferably 3 to 5 times daily. Insome embodiments, the interval of time between each application of theBi₂S₃—CdS particles may be about 1-5 minutes, 1-30 minutes, 30 minutesto 60 minutes, 1 hour, 1-2 hours, 2-6 hours, 2-12 hours, 12-24 hours,1-2 days, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 1 week, 2weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10weeks, 15 weeks, 20 weeks, 26 weeks, 52 weeks, 11-15 weeks, 15-20 weeks,20-30 weeks, 30-40 weeks, 40-50 weeks, 1 month, 2 months, 3 months, 4months, 5 months, 6 months, 7 months, 8 months, 9 months, 10 months, 11months, 12 months, 1 year, 2 years, or any period of time in between.

In one or more embodiments, the aforementioned method in any of itsembodiments may prevent or reduce growth of a gram-negative bacteriumwhich is at least one selected From the group consisting ofAcinetobacter baumannii, Enterobacter aerogenes, Escherchia coli,Klebsiella oxytoca, and Klebsiella pneumoniae.

Acinetobacter baumannii (A. baumannii) is an almost round, rod-shapedgram-negative bacterium which can be an opportunistic pathogen inhumans, affecting people with compromised immune systems, and isbecoming a major cause to hospital-derived infections (nosocomialinfections) in medical facilities. Enterobacter aerogenes (E. aerogenes,also known as Klebsiella aerogenes), is a rod-shaped, gram-negativebacterium. E. aerogenes a nosocomial and pathogenic bacterium thatcauses infections and the treatment of E. aerogenes caused infection isoften complicated by their inducible antibiotic resistance mechanisms.Pathogenic strains of Escherchia coli (E. coli) can causegastroenteritis, urinary tract infections, neonatal meningitishemorrhagic colitis, and Crohn's disease. Common signs and symptomsinclude severe abdominal cramps, diarrhea, hemorrhagic colitis,vomiting, and sometimes fever. Klebsiella oxytoca (K. oxytoca) is agram-negative, rod-shaped bacterium that nay cause colitis and sepsis.K. oxytoca is capable of acquiring antibiotic resistance. Klebsiellapneumoniae (K. pneumoniae) is a gram-negative, rod-shaped bacteriumclosely related to K. oxytoca.

The method disclosed herein in any of its embodiments may be effectiveon other pathogenic gram-negative bacteria including, but not limitedto, Klebsiella granulomatis, Klebsiella variicola, Acinetobactercalcoaceticus, Acinetobacter calistiniresistens, Acinetobacter defluvii,Acinetobacter haemolyticus, Acinetobacter junii, Acinetobacter lwoffii,Acinetobacter pitii, Acinetobacter schindleri, Acinetobacter soli,Pseudomonas aeruginosa, Neisseria meningitidis, Neisseria gonorrhoeae,Pseudomonas pseudomallei, Treponema pallidum, Mycobacteriumtuberculosis, Salmonella spec., alpha-Proteobacteria (particularlyAgrobacterium spec.), beta-Proteobacteria (particularly Nitrosomonasspec.), Aquabacterium spec., Gammaproteobacteria, Stenotrophomonas spec.(particularly S. maltophilia), Xanthomonas spec. (X. campestris),Neisseria spec., and Haemophilus spec.

In one or more embodiments, the aforementioned method in any of itsembodiments may prevent or reduce growth of a gram-positive bacteriumwhich is at least one selected from the group consisting ofStaphylococcus aureus, Staphylococcus epidermis, and MRSA.

Staphylococcus aureus (S. aureus) is a grain-positive, round-shapedbacterium which is a corn cause of skin infections, atopic dermatitis,bone and joint infections including infections from joint replacementsurgeries, and other medical devices implanted in the body or on humantissue. Staphylococcus epidermidis (S. epidermidis) is a gram-positivebacterium, which is known for its ability to form biofilms that grow onmedical devices and surgical implants. MRSA, known asmethicillin-resistant Staphylococcus aureus, refers to a group ofgram-positive bacteria that are genetically distinct from other strainsof Staphylococcus aureus. MRSA is any strain of S. aureus that hasdeveloped multiple drug resistance to beta-lactam antibiotics, throughhorizontal gene transfer and natural selection. Treatment of MRSA can bechallenging and delays are often fatal.

The method disclosed herein in any of its embodiments may be effectiveon other pathogenic gram-positive bacteria including, but not limitedto, Staphylococcus auricularis, Staphylococcus capitis, Staphylococcuscaprae, Staphylococcus cohnii, Staphylococcus delphini, Staphylococcusfelis, Staphylococcus gallinarum, Staphylococcus haemolyticus,Staphylococcus hominis, Staphylococcus hyicus, Staphylococcuslugdunensis, Staphylococcus pettenkoferi, Staphylococcuspseudintermedius, Staphylococcus rostri, Staphylococcus saccharolyticus,Staphylococcus saprophyticus, Staphylococci schleiferi, Staphylococcusvitulinus, Staphylococcus warneri, Staphylococcus xylosus, Streptococcuspyogenes Corynebactertum spp. (particularly C. tenuis, C. diphtheriae,and C. minutissimum), Micrococcus spp. (particularly M. sedentarius),Bacillus anthracis, Streptococcus spec. (particularly S. gordonii, andS. mutans), Actinomyces spec. (particularly A. naeslundii), andActinobacteria (particularly Brachybacterium spec.).

In certain embodiments, preventing or reducing growth of a microorganismon the surface may be evaluated by measuring microbial counts of thesurface before and/or at least 30 minutes, preferably at least 1 hour,more preferably at least 2 hours after applying the surface with theBi₂S₃—CdS particles via the method described herein in any of itsembodiments. For example, the number of viable microorganisms is countedusing a slide count method and/or a direct culture method (plate count).

The “slide count” method utilizes a microscope slide in a chamber thatis especially designed to enable cell counting. A total number of cellsin a sample can be determined by looking at the sample under amicroscope and counting the number manually. A number of viable cellscan also be determined using the slide count method if a viability dyeis added to the sample. Exemplary viability dyes include, but are notlimited to, Trypan Blue, Calcein-AM, Erythrosine B, propidium iodide,and 7-aminoactinomycin D.

“Colony-forming unit (CFU)” refers to a unit used to estimate the numberof viable bacteria or fungal cells in a sample. The purpose of directculture method (plate count) is to estimate the number of cells presentbased on their ability to give rise to colonies under specificconditions of nutrient medium, temperature and time. Theoretically, oneviable cell can give rise to a colony through replication. A samplesolution of microbes at an unknown concentration is often seriallydiluted in order to obtain at least one plate with a countable number ofCFUs. Counting colonies is performed manually using a pen and aclick-counter, or automatically using an automated system and a softwaretool for counting CFUs.

In other embodiments, preventing or reducing growth of a microorganismon a surface may be evaluated by conducting disk diffusion tests of thesurface before and/or at least 30 minutes, preferably at least 1 hour,more preferably at least 2 hours after applying the surface with theBi₂S₃—CdS particles via the method described herein in any of itsembodiments.

The disk diffusion method (or agar diffusion test, or Kirby-Bauer test)evaluates the effectiveness of antibiotics on a specific microorganismby testing the extent to which bacteria are affected by thoseantibiotics. In this test, samples containing antibiotics are placed onan agar plate where bacteria have been placed, and the plate is left toincubate. If an antibiotic stops the bacteria from growing or kills thebacteria, there will be an area around the sample where the bacteriahave not grown enough to be visible. This is called a zone ofinhibition. Thus, the effectiveness of antibiotics can be measured usingtheir zone of inhibition.

Preventing or reducing growth of a microorganism on a surface may beunderstood to indicate a reduction of the number of microorganism cellson the surface after applying the Bi₂S₃—CdS particles onto the surface.In some embodiments, the number of microorganisms on the surfacecharacterized by a microbial count is reduced by at least 10%,preferably at least 20%, more preferably at least 30%, more preferablyat least 40%, more preferably at least 45%, more preferably at least50%, more preferably at least 55%, more preferably at least 60%, morepreferably at least 65%, more preferably at least 70%, more preferablyat least 80%, more preferably at least 90%, or more preferably at least95%, with respect to use of an untreated control surface. Ideally, thegrowth of microorganisms on the surface may be completely or almostcompletely prevented.

Alternatively, preventing or reducing growth of a microorganism on asurface may be understood to indicate an increase of the size of zone ofinhibition on the surface after applying the Bi₂S₃—CdS particles ontothe surface. In some embodiments, the zone of inhibition ofaforementioned one or more microorganisms on the surface is increased byat least 50%, preferably at least 75%, more preferably at least 100%,more preferably at least 150%, more preferably at least 200%, morepreferably at least 250%, more preferably at least 300%, more preferablyat least 350%, more preferably at least 400%, more preferably at least450%, more preferably at least 500%, more preferably at least 600%, ormore preferably at least 800%, with respect to use of an untreatedcontrol surface.

The examples below are intended to further illustrate protocols forpreparing, characterizing Bi₂S₃—CdS particles, and uses thereof, and arenot intended to limit the scope of the claims.

EXAMPLE 1

Preparation of Bi₂S₃—CdS Nanospheres

All chemicals used were purchased from commercial sources. 0.243 g ofbismuth nitrate (Bi(NO₃)₃.5H₂O) and 0.291 g cadmium nitrate(Cd(NO₃)₂.4H₂O) was weighed and transferred into a teflon lined vial,and 20 mL of ethylene glycol was added to this mixture, which wasfollowed by addition of thiourea (0.228 g) and polyvinylpyrrolidone (PVP, 0.4 g). The reaction mixture was stirred at room temperature for 15-20minutes Teflon lined vial was closed in teflon lined autoclave and themixture was heated at 200° C. for 24 hours. The flask was cooled to roomtemperature and the precipitate was centrifuged, washed with deionizedwater and then with ethanol. The product was dried in the oven for 24hours at 60° C.

EXAMPLE 2

Characterizations of Bi₂S₃—CdS Nanospheres

The morphologies of Bi₂S₃—CdS nanospheres were examined by scanningelectron microscopy (SEM, FEI INSPECT S50). The crystallinity andcrystal phases of as-synthesized Bi₂S₃—CdS were studied by X-raydiffractometer (XRD Rigaku, Japan) measured with Cu-Kα radiation(λ=1.5418 Å) in the range of 10-80° with 1°/min scanning speed. UV-Visdiffuse reflectance spectrum of Bi₂S₃—CdS was recorded on a diffusereflectance UV-Vis spectrophotometer (JASCO V-750). Micromeritics ASAP2020 PLUS nitrogen adsorption apparatus (USA) was employed for BETsurface area determination. Before analysis, samples were degassed at180° C. Surface area was determined using N₂ adsorption data in therelative pressure (P/P₀) range of 0.05-0.3.

EXAMPLE 3 Photocatalytic Activity

The photocatalytic activity of Bi₂S₃—CdS was evaluated throughphotocatalytic degradation of methyl orange and methyl green under UVlight irradiation for 120 min using Xenon lamp (300 W) as light source.In each experiment (carried out separately for each dye) 50 mg ofBi₂S₃—CdS was dispersed in 50 mL of aqueous dye solution of methylorange (10 mg/L) or methyl green (14 mg/L). In order to ensure theadsorption-desorption equilibrium between the photocatalyst and dye,solution was stirred in dark for 1 hour and then illuminated under Xenonlamp (300 W). After 15 min time interval, 4 mL of the suspension wascollected and centrifuged to remove Bi₂S₃—CdS catalyst. Theconcentration of dye was assessed using a UV-Visible spectrophotometer(JASCO V-750) by measuring the absorbance of dyes at their respectivewavelength. The degradation efficiency was calculated as:

Degradation rate (%)=(C ₀ −C)/C ₀×100   (equation 1)

where C₀ is the initial concentration of the methyl orange or methylgreen and C is the time-dependent concentration of methyl orange ormethyl green after each irradiation (see FIG. 6).

EXAMPLE 4 Antibacterial Activity Test

Gram positive and Gram negative bacteria reference strains ATCC(American Type Culture Collection) were procured from Department ofMicrobiology, College of Science, IAU, Dammam, which included:Escherchia coli ATCC25922, Klebsiella oxytoca ATCC700324, Klebsiellapneumoniae ATCC100324, Acinetobacter baumannii ATCCmra747, Enterobacteraerogenes ATCC13048, Staphylococcus epidermis ATCC12228, Staphylococcusaureus ATCC24213, and MRSA 1 and MRSA 2 (clinical isolates). The strainswere maintained on agar slants at 4° C. and activated at 37° C. for 24 hon nutrient agar prior to any test.

EXAMPLE 5

Preparation of Bi₂S₃—CdS Nanomaterial

A known amount of Bi₂S₃—CdS nanomaterial was dissolved in 5% DMSO withcontinuous stirring to obtain a homogenized solution. The homogenizedsuspension was further diluted to obtain solutions each havingconcentrations of 0.31, 0.625, 1.25, 2.5, and 5 mg/mL Bi₂S₃—CdS,respectively.

EXAMPLE 6 Inoculum Preparation

Test strains were grown overnight at 37° C. in Mueller Hinton Broth andthe turbidity was adjusted to 0.5 McFarland units (approximately 10⁶colony forming units (CFUs)/mL).

EXAMPLE 7 Zone Inhibition Method

100 μL of prepared inoculums of each reference strain was uniformlyspread over fresh nutrient agar plates with a sterile spreader toachieve a confluent growth. Seven wells of 6 mm diameter were punchedwith the assistance of a sterile cork borer. 50 μL test solution ofdifferent concentrations was added in the wells of the inoculated agarplates for each test organism. DMSO was used as a negative control.Ampicillin at a concentration of 30 μg/mL was used as a positivecontrol. The plates were allowed to stand for 1 h at room temperaturefor diffusion of the test solution into agar and incubated at 37° C. for24 h. Clear zone of inhibition around each well was measured. Eachexperiment was performed in triplicates.

EXAMPLE 8 Determination of Minimal Bactericidal Concentrations (MBCs)

MBC (Minimum Bactericidal Concentration) for Bi₂S₃—CdS nanomaterial wasalso evaluated by the micro-broth dilution method. Both gram negativeand positive bacterial strains were used in this test. Controlexperiments were carried out in presence of ampicillin and in absence ofBi₂S₃—CdS nanomaterial as positive and negative controls, respectively.In general, 10 mL nutrient broth medium supplemented with Bi₂S₃—CdSnanomaterial at concentrations of 0.31, 0.625, 1.25, 2.5, and 5 mg/mLwas prepared separately. Each set was inoculated with 100 μL ofovernight bacterial suspension (10⁶ CFU/mL) and were incubated for 24hours with shaking at 35° C.±2° C. After overnight incubation, 10 μL ofeach set was streaked out on a nutrient agar plate and further incubatedat 35° C.±2° C. for 24 hours. Viable bacterial colonies were counted andrecorded by the naked eye to determine the MBC as the lowestconcentration that blocked bacterial growth. The experiments werecarried out in triplicate, and averages were reported.

EXAMPLE 9

Bi₂S₃—CdS nanospheres were prepared by solvothermal method. The preparedBi₂S₃—CdS nanoparticles were characterized by X-ray powder diffraction(XRD), scanning electron microscope (SEM), UV-Vis diffuse reflectancespectrophotometer, and BET surface area analysis. The BET surface areaof Bi₂S₃—CdS nanospheres was determined to be 11.29 m²/g (pore size:23.69 nm; pore volume: 0.0683 cm³/g). The potential application ofBi₂S₃—CdS nanoparticles was evaluated for the photocatalytic degradationof environmental pollutants such as methyl orange, and methyl green. Itwas observed that nanoparticles exhibited good photocatalyticdegradation of methyl orange and methyl green.

Additionally, antimicrobial activity of Bi₂S₃—CdS nanoparticles wasevaluated, against Gram-positive and Gram-negative microorganisms.Antibacterial activity results revealed that the tested nanoparticlesacted as an excellent antibacterial agent against both Gram-positive andGram-negative bacteria. The concentration-dependency of antimicrobialactivities of nanoparticles against Gram-negative bacteria was observed.Greater inhibition zone (22 mm) against Acinetobacter baumannii wasachieved at the concentration of 5 mg/mL and zone of 8 mm at 0.31 mg/mLaccompanied with MBC value of 1.25 mg/mL. The lowest activity was seenagainst Klebsiella pneumoniae with 16 mm zone of inhibition and MBC atthe concentration of 5 mg/mL. The nanomaterial proved to be moreeffective on Gram-negative bacteria with respect to positive control(ampicillin at 50 μg/mL) to which many bacteria strains tested wereresistant.

Amongst the Gram-positive strains, the nanomaterial was most effectiveagainst the Staphylococcus aureus with 22 mm zone of inhibition at theconcentration of 5 mg/mL and 12 mm zone of inhibition at 0.31 mg/mLaccompanied with MBC value of 1.25 mg/mL. The positive control(ampicillin 50 μg/mL) also showed 26 mm zone of inhibition. Thenanomaterial also showed activities against Staphylococcus epidermis andMRSA isolates with considerable zone of inhibition as compared to thepositive control (ampicillin 50 μg/mL), which was not active for thesemicroorganisms.

Our results indicated that nanomaterials disclosed herein were effectiveagainst both Gram-positive and Gram-negative bacterial strains, henceoffering an antimicrobial with a broad spectrum activity.

1. A method for degrading an organic pollutant, the method comprising:contacting Bi₂S₃—CdS particles with an aqueous solution comprising theorganic pollutant to form a mixture; illuminating the mixture with alight at a wavelength in a range of 200-700 nm for 0.1-6 hours therebydegrading the organic pollutant; wherein: the Bi₂S₃—CdS particlescomprise bismuth(III) sulfide and cadmium(II) sulfide; the Bi₂S₃—CdSparticles are in the form of spheres; and the organic pollutant ispresent in the aqueous solution at a concentration of 1-1,000 mg/Lrelative to a total volume of the aqueous solution.
 2. The method ofclaim 1, wherein an atomic ratio of bismuth to cadmium in the Bi₂S₃—CdSparticles is in a range of 0.5:1 to 4:1, and an atomic ratio of sulfurto bismuth in the Bi₂S₃—CdS particles is in a range of 3:2 to 8:1. 3.The method of claim 1, wherein the Bi₂S₃—CdS particles are in the formof spheres with an average diameter of 0.3-5 μm.
 4. The method of claim1, wherein the Bi₂S₃—CdS particles have a BET surface area of 5-25 m²/g,a pore size of 10-50 nm, and a pore volume of 0.02-0.2 cm³/g.
 5. Themethod of claim 1, wherein an amount of the Bi₂S₃—CdS particles in themixture is in a range of 0.1-10 g/L relative to a total volume of themixture.
 6. The method of claim 1, wherein at least 30% by mole of theorganic pollutant is degraded within 2 hours of illuminating.
 7. Themethod of claim 1, wherein the organic pollutant comprises methylorange, methyl green, or both.
 8. A method for preventing or reducinggrowth of a microorganism on a surface, the method comprising: applyingBi₂S₃—CdS particles onto the surface; wherein: the Bi₂S₃—CdS particlescomprise bismuth(III) sulfide and cadmium(II) sulfide; the Bi₂S₃—CdSparticles are in the form of spheres; and the Bi₂S₃—CdS particles are incontact with the surface for 1-24 hours.
 9. The method of claim 8,wherein an atomic ratio of bismuth to cadmium in the Bi₂S₃—CdS particlesis in a range of 0.5:1 to 4:1, and an atomic ratio of sulfur to bismuthin the Bi₂S₃—CdS particles is in a range of 3:2 to 8:1.
 10. The methodof claim 8, wherein the Bi₂S₃—CdS particles have a BET surface area of5-25 m²/g, a pore size of 10-50 nm, and a pore volume of 0.02-0.2 cm³/g.11. The method of claim 8, wherein the Bi₂S₃—CdS particles are appliedonto the surface as a solution comprising a solvent and 1 μg/mL to 50mg/mL of the Bi₂S₃—CdS particles relative to a total volume of thesolution.
 12. The method of claim 11, wherein the solvent comprisesdimethyl sulfoxide and water.
 13. The method of claim 8, wherein theBi₂S₃—CdS particles are applied onto the skin of a subject as anantimicrobial cream comprising 0.01 wt %-50 wt % of the Bi₂S₃—CdSparticles relative to a total weight of the antimicrobial cream.
 14. Themethod of claim 8, wherein the microorganism is at least onegram-negative bacterium selected from the group consisting ofAcinetobacter baumannii, Enterobacter aerogenes, Escherchia coli,Klebsiella oxytoca, and Klebsiella pneumoniae.
 15. The method of claim8, wherein the microorganism is at least one gram-positive bacteriumselected from the group consisting of Staphylococcus aureus,Staphylococcus epidermis, and MRSA.
 16. Bi₂S₃—CdS particles, comprising:bismuth(III) sulfide; and cadmium(II) sulfide, wherein the Bi₂S₃—CdSparticles are in the form of spheres with an average diameter of 0.3-5μm.
 17. A method of preparing the Bi₂S₃—CdS particles of claim 16, themethod comprising: mixing a bismuth(III) salt, a cadmium(II) salt, andan optionally substituted thiourea with a solvent in the presence ofpolyvinylpyrrolidone to form a reaction mixture; and heating thereaction mixture in an autoclave at a temperature of 100-300° C. for2-48 hours thereby forming the Bi₂S₃—CdS particles.
 18. The method ofclaim 17, wherein an atomic ratio of bismuth to cadmium in the reactionmixture is in a range of 0.5:1 to 4:1.
 19. The method of claim 17,wherein a molar ratio of the optionally substituted thiourea to thebismuth(III) salt is in a range of 2:1 to 10:1.
 20. The method of claim17, wherein the optionally substituted thiourea is thiourea of formulaSC(NH₂)₂.